A transistor, such as a high-voltage or power transistor, may be laterally arranged (as opposed to vertically arranged) when used with smaller currents. The lateral arrangement may be convenient for low profile designs or for the integration of multiple transistor devices on a substrate.
During normal operation of a transistor, electric fields are generated with current flow in the upper layer(s) of the device. Additional electric fields are also generated in the underlying substrate of the transistor as well. In many lateral transistor designs, these electric fields influence each other, often creating performance issues.
One solution to the interaction of the electric fields includes forming the transistor components on a lightly doped substrate and coupling the lateral electric field to the top layer. With this solution, relatively long lateral components may be used to offset the potential reduction in the substrate. Additionally, wider edge structures may also be used with these high-voltage devices. The use of the longer and/or wider components may result in performance and/or design issues.
Another solution to the interaction of the electric fields includes selectively removing substrate from under some lateral transistor components. The resulting air insulator may reduce or remove interfering electric fields. However, the air insulator may be relatively deep to achieve a desired blocking voltage for the device. Structural strength of the device may be compromised due to the air gaps within the device, particularly if transistor components are formed on a membrane that is cantilevered over a relatively long air gap span. Further, the air gaps may be susceptible to penetration of solder, adhesives, or other materials during manufacturing. This may lead to an undesirable change in the blocking voltage of the device.